Endocrine System Part 1

Endocrine System The endocrine system is the “other” control system of the body – Works closely with nervous system – Connection is hypothalamus -> pituitary gland Any organ that releases signal molecules (hormones) into the blood is part of the endocrine system – Many organs scattered throughout the body

Hormones A hormone is any signal molecule that enter the blood and attaches to a target cell’s receptors Two major types of hormones: Steroid hormones and nonsteroid hormones – Steroid hormones are made from cholesterol and include testosterone & estrogen – Most hormones are nonsteroid

Steroid vs. Nonsteroid A steroid hormone is lipid- soluble – Therefore can pass through cell membrane – Binds to molecules inside cytoplasm or nucleus to change cell behavior A nonsteroid hormone must bind to receptor molecules on the surface of the cell membrane – These receptors release second messengers that enter the nucleus and change the cell behavior

Negative Feedback Loop Essential core of endocrinology is the negative feedback loop In a negative feedback loop, the product of a signal blocks its own signal – A increases B, but B decreases A – Creates an optimal amount of signal and product Most hormones block the effect or signal that stimulate their own release

Endocrine Signaling Many organs are part of at least one signal pathway – Technically the heart, liver, fat tissue, thymus, etc. are all part of the endocrine system Many (not all) endocrine organs receive signals from the pituitary gland – The pituitary gland is directly attached to the hypothalamus – The HPA axis is the hypothalamus-pituitary-adrenal gland signal pathway

Endocrine Topics (2 days) Hypothalamus Pituitary Adrenal Cortex Adrenal Medulla Thyroid Parathyroid Pancreas Gonads Bonus hormones

Hypothalamus The hypothalamus is in the center of the brain and receives signals from the rest of the brain – Hypothalamus is also outside the blood-brain barrier so it can monitor blood temperature, nutrient and ion levels, etc. To affect the body, the hypothalamus sends hormonal and nervous signals to the pituitary gland

Pituitary Gland The pituitary gland has a front and back portion that are both for hormonal signals The anterior pituitary signals the other glands of the body The posterior pituitary handles the release of two other hormones: ADH and oxytocin

ADH: Anti-diuretic Hormone A diuretic is anything that increases urination – Alcohol, caffeine, etc Anti-diuretic hormone (synonym: vasopressin) is released to conserve water in the body – Changes the behavior of the kidneys Kidneys reabsorb more water from urine when signaled with ADH – Failure to release ADH means kidneys urinate water even when you are dehydrated

Oxytocin Oxytocin in women promotes lactation and is involved in childbirth – Was thought to be only in women Oxytocin also has effects on the brain in both men and women – Primarily promotes bonding and affection – Is released during orgasm No strings attached sex? Not if your posterior pituitary can help it!

Anterior Pituitary The anterior pituitary releases hormones that primarily stimulate other glands: – TSH: Thyroid – ACTH: Adrenal glands – FSH & LH: Gonads – Growth Hormone (hGH): long bones & muscles

Growth Hormone Growth hormone stimulates growth in the long bones at the growth plate – Deficiency of growth hormone during youth can cause pituitary dwarfism – Excess can make you very tall… Works by stimulating bones to grow and also increases metabolism

Adrenal Cortex The adrenal glands are a multi- layered gland – Adrenal cortex releases cortisol and aldosterone (and similar hormones) Aldosterone helps conserve sodium and potassium -Also helps keep sodium concentration higher than potassium -Produced via signals from the kidneys

Cortisol and Stress Cortisol is released in response to ACTH from the pituitary glans – This signal originates from the hypothalamus when the brain is stressed Cortisol increases available energy for the body but also blocks the immune system and healing mechanisms – Long-term effects of cortisol include weight loss, bone and muscle wasting and chronic illnesses

Adrenal Medulla The adrenal medulla releases epinephrine (adrenaline) when stimulated by the sympathetic nervous system Epinephrine increases heart rate (by stimulating SA node), dilates passageways of lungs, increases blood flow to muscles, and increases alertness by stimulating midbrain

HPA Axis Stress Response When the frontal lobes of the brain detect a dangerous situation, they signal the hypothalamus with this information The hypothalamus has two responses: – Stimulates ACTH release from the pituitary for cortisol release (long-term stress) – Stimulates the adrenal medulla for epinephrine (immediate stress) These are safety mechanisms to prevent death by starvation or by being eaten by wolves

See you Wednesday! Please remember to check your blackboard messages!